Electrophotographic processes using disazo pigments

ABSTRACT

Electrophotographic processes using as the photoconductive material disazo pigment present as very small particles in an amount up to 10 percent of the total weight of the pigment particles plus the charge transport material.

Champ et a1.

ELECTROPHOTOGRAPHIC PROCESSES USING DISAZO PIGMENTS Inventors: Robert Bruce Champ; Meredith David Shattuck, both of San Jose, Calif.

Related U.S. Application Data Continuation-impart of Ser. No. 129,635, March 30,

1971, abandoned.

Assignee:

U.S. C1. 96/l.5; 96/l.6; 260/148 Int. Cl. G03G 5/06; G036 13/22 Field of Search 96/1.5, 1.6; 260/148 Aug. 5, 1975 [56] References Cited UNITED STATES PATENTS 3,591,374 7/1971 Seus 96/l.6 3,634,079 1/1972 Champ et al. 96/1.6 X 3,684,548 8/1972 Contois 96/16 X 3,775,105 11/1973 Kukla 96/].5 X

Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or Firm-Joseph G. Walsh [5 7] ABSTRACT Electrophotographic processes using as the photoconductive material disazo pigment present as very small particles in an amount up to 10 percent of the total weight of the pigment particles plus the charge transport material.

11 Claims, No Drawings ELECTROPHOTOGRAPHIC PROCESSES USING DISAZO PIGMENTS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrophotographic processes and photoconductive plates used therein. In particular it is concerned with plates comprising certain disazo pigments.

2. Description of Prior Art U.S. Pat. No. 3,384,566 is concerned with photoelectrophoresis. The patent discloses certain disazo compounds (Pyrazolone red B and Diane Blue in column 13) for use in photoelectrophoresis.

U.S. Pat. No. 3,384,488 is also concerned with photoelectrophoresis. The disazo compound Diane Blue is disclosed therein (see Example (XXII). That patent also discloses milling of the pigment to particles of less than 1 micron size (see column 12, line 58).

U.S. Pat. No. 3,663,636, concerned with a binder type photoconductive element, suggests micropulverizing organic photoconductors.

In other places in the prior art, milling of photoconductor to obtain small particle size is also shown.

No prior art reference of which we are aware, however, suggests the advantages obtained in the present invention, which involves the use of certain selected disazo compounds as very small sized particles in electrophotographic reproduction processes, which are distinguishable from photoelectrophoresis in that selective photoconductivity, and not migration of the pigment, is involved.

SUMMARY OF THE INVENTION According to the present invention, electrophotographic plates are prepared comprising certain selected disazo pigments. The disazo pigments useful in the present invention include those having the structural formula I Y X HZN h wherein A is selected from the group consisting of:

wherein R is selected from the group consisting of lower alkyl and E-O-lower alkyl,

and X and Y are each selected from the group consisting of: H,CI-I ,OCH ,OC H =,,OI-I,CL and Br.

It has now been discovered that when pigments having the formula disclosed above are present in an electrophotographic plate in particle size less than about 5 microns in diameter, and preferably less than 1 micron in diameter, they are very effective charge generators. The particles should be dispersed in a charge transport medium, and present as individual particles not touching each other; this occurs when the pigment particles are present in an amount up to 10% of the total weight of the pigment particles plus the charge transport medium. As little as 1 percent by weight can be used in some cases, but in general from about 3 to about 6 percent is preferred. Alternatively, the particles may be overcoated by a charge transport layer. In either case, however, there is injection of charge from the pigment to the transport material, in distinction over the prior art.

Compounds of the above formulas may all be prepared by well-known procedures picking the properly substituted starting materials in each case, and carrying out the synthesis by methods in accordance with the teachings of the prior art.

It must be emphasized that the particles of pigment are not dissolved; i.e., they are not present as single molecules in a solution. Rather they are present as polymolecular aggregates. The use of the word pigment to describe the materials is in accord with this fact, since the word pigment in the art is usually used to describe a colored particle which is not in solution, as contrasted to the word dye, which is used to describe a colored material which is in solution.

As mentioned previously, the pigment size should be less than 5 microns in diameter. Preferably the pigment size is less than about 1 micron in diameter. Furthermore, there is some evidence to suggest that in at least some cases it is advantageous that the particle sizes are close to uniform.

In accordance with the present invention, the pigments may be used in the form of a thin layer on a conductive substrate. The layer may be overcoated with a charge transport layer. Systems of this sort are described in U.S. Patent application Ser. No. 99,647, filed Dec. 18, 1970, by Herrick and Shattuck.

The pigments are present in a charge transport binder medium, which may be either photoconductive per se or not photoconductive per se. There are many binders known to the prior art as being useful in the making of photoconductive plates. They include numerous resins and the like. Many such materials are mentioned, for example, in U.S. Pat. Nos. 3,121,006 and 3,121,007. Among the charge transport resins found useful in the present invention, polyesters have been particularly outstanding, for example, Myler adhesive 49,000, which is duPonts trademark for a 60/40 copolymer of ethylene terephthalate and ethylene isophthalate. Polyketones are also useful, e.g., PK 252, Union Carbides trademark for a polyketone. It is not, however, necessary that the binder be a resin. For example, U.S. Pat. No. 3,406,063 lists non-polymeric coating-forming materials which may also be used in the present invention. It should also be mentioned that sucrose benzoate gives excellent results when used as a binder in the present invention.

The binder material may also be photoconductive per se. A particularly useful photoconductive binder is the photoconductor described and claimed in U.S. Pat. No. 3,484,237 of Shattuck and Vahtra. This patent describes a photoconductive material which is formed from polyvinyl carbazole and trinitrofluorenone.

To increase the photoconductivity of some of the above-described photoconductive pigments, there may be incorporated in the pigment either a sensitizer or an activator which is also known as an electron acceptor or, in some cases, when the photoconductor is an electron acceptor, an electron donor. Examples of such dye sensitizers and activators are set forth in U.S. Pat. Nos. 3,037,861, 3,169,060, and 3,287,113. In addition, when it is desired to have the photoconductive element exhibit persistent conductivity, the dye sensitizer and activator combinations described in U.S. Pat. Nos. 3,512,966 may be used in the preparation of such photoconductive elements.

Many of the pigments useful in the present invention have been listed in the Colour Index published jointly by the Society of Dyers and Colourists in England and the American Association of Textile Chemists and Colorists, Lowell, Massachusetts, U.S.A., Second Edition, 1956. In some cases below, they are referred to by their Color Index number, or Cl.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

EXAMPLES EXAMPLE 1 The pigment used in the following example is called Diane Blue (C.I. 21,180). Chemically it is 3,3 dimethoxy-4,4 diphenyl bis-( 1 '-azo-2 'hydroxy-3 naphthanilide). A 5 percent suspension of Diane Blue in tetrahydrofuran (TI-IF) was attrited to a particle size of about 1 micron by grinding with steel balls.

This mixture was added at an 8 percent by weight level of addition to a mixture of 1 part Mylar adhesive 49,000 and 1 part 2,4,7 Trinitro-9-fluorenone (TNF). This total mixture is thoroughly dispersed by roller milling and is then coated at 25 percent solids on aluminized Mylar giving a thickness of about l5,u.. (Mylar is duPonts brand of polyethylene terephthalate.)

This photoconductive plate was capable of making excellent images at photographic speeds 2 to 4 times that of commercially available selenium with a tungsten-iodide light source.

EXAMPLE 2 The 5 percent Diane Blue TI-IF attributed mixture as described in Example 1 is diluted to 2 percent by addition of THF and this solution is coated on aluminized Mylar subbed with a 0.211. coating of Elvamide 8061 to promote adhesion and I flexibility. Thickness of the Diane Blue layer is about O.5p.. (Elvamide 8061 is an alcohol soluble polyamide resin from duPont.) The pigment is present at about 5 percent concentration by weight.

To this is coated the polyester resin/TNF mixture described in the above example at a thickness of about 10p This photoconductive plate was capable of photosensitivity equal to or above that described in Example 1.

EXAMPLE 3 EXAMPLE 4 A layered system as described in Example 2 was used, except the top layer consists of 20 percent by weight TNF in polyvinylcarbazole. Thicknesses are the same as described in Example 2, with the pigment present at about 5 percent concentration by weight. Images were obtained at -2 times that of commercially used organic photoconductors using green light.

EXAMPLE 5 The preferred pigment for use in the present invention is called Chlorodiane Blue. It differs from Diane Blue in that it has chloro groups, instead of methoxy groups, on the benzidine nucleus. The synthesis of Chlorodiane Blue is outlined below. It is illustrative of the general type of synthesis which may be used to prepare structurally related pigments.

10g (.04 mol) of 3,3'dichlorobenzidene is diazotized 15C in 150cc 18 percent I-ICl by dropwise addition of 5N NaNO (0.08 mol). The solution is checked for excess nitrite to assure complete reaction by use of the indicator 3,7-thiaxanthene diamine 5,5-dioxide in dilute HCl. The unreacted 3,3'-dichlorobenzidene is filtered off, and to the filtrate is added cc H BF 4 (48 percent) and the mixture is stirred for 20 minutes. The pale yellow precipitate is filtered off, washed with ethanol and ether and dried. The solid is then recrystallized from 400cc water at 55C using charcoal.

8.5g (.02 mol) of the solid diazonium salt obtained above is dissolved in 200 ml dimethyl formamide (DMF) and added to a solution of 1 1.6g (.044 mol) of 2-hydroxy-3-naphthanilide coupler in 1500 ml DMF at l0l5"C. A solution of 20g sodium acetate in 300 ml water is added slowly with vigorous stirring. The mixture is stirred at room temperature for 1.5 hours and filtered. The compound is then stirred in 21. water for at least 8 hours, filtered and washed with water. The solid is then stirred in 1.51. DMF for 1 hour, filtered, washed with DMF and again stirred in DMF overnight, filtered, washed with DMF, acetone and ether to remove all DMF and the compound is then dried under vacuum at 50C. Yield -l3.0g.

EXAMPLES 6 to 2 In the following set of Examples, pigments lettered A through G were used. Their structures are given below.

The electrophotographic data obtained by the use of Pigments A through G are shown in the following Tables I through III. 1

In Table I below, the milled pigments, at a 10 percent by weight concentration, were dispersed in a photoconductive resin charge transport binder. The binder was 20 percent by weight trinitrofluorenone and 80 percent by weight polyvinyl-carbazole. The binder-pigment mixture was again coated on a conductive substrate. The expression full Tungsten used below means that the illumination was from a tungsten halogen lamp, 75 watts, 28 volts at a distance of 15 cm. (NDS refers to the use of a neutral density screen, and 0G to the use of an opal glass diffuser.)

In Table II below, a 10 percent by weight of the milled pigment was dispersed ina resin binder which was a 1:1 by weight mixture of trinitrofluorenone and Mylar adhesive 49,000. The mixture was coated on a conductive substrate.

TABLE II EXAMPLE PIGMENT LIGHT DECAY CHARGE ACCEPTANCE NUMBER DESIGNATION T V2 (1.16 NDS-IOG) (volts) (sec) l4 A (H) 9.0 2.45 1060 800 15 B (CH 7.5 1.65 900 940 16 C (OCH 8.1 6.0 980 900 17 D (CI) 17.0 10.0 1150 1200 18 E (OCH 1.6 0.8 700 900 19 F (CH 2.5 0.45 660 840 20 g G (CI) 4.0 0.8 530 1050 No pigment added Too slow to measure Control 7 8 In Table III below, the milled pigment, at a percent TABLE IV by weight level, wasadded to QPhOIOCOI'IdIIJCtIVB resin EXAMPLE MOMENT ELECTROMETER T V2 (Fun binder which was a 1:1 molar mixture of trinitrofluore- A none and polyvinyl carbazole (based on the monomer NUMBER TR CT RE CHARGE A Tun sten) ACCEPTANCE weight). 5

29 D 1,000 v 0.25 sec 30 c 900 v 0.08 sec 31 B 530 v 0.1 sec 32 G 265 V 0.08 sec 33 E 490 V 0.05 sec 34 F 530 V 0.07 sec TABLE III EXAMPLE PIGMENT LIGHT DECAY CHARGE ACCEPTANCE NUMBER DESIGNATION T V2 (1.16 NDS+OG) (volts) (sec) (-1-) 21 A (H) 0.9 0.7 I 620 700 22 B (CH 1.7 0.65 540 760 23 C (OCH 1.1 1.1 600 600 24 D (CI) 1.6 0.9 580 580 25 E (OCH 1.9 0.65 320 450 26 F (CH 1.43 0.35 800 580 27 G (C1) 2.6 0.25 400 700 28 No Pigment 1.6 1.0 680' 780 added EXAMPLES 29-34 The following pigments were milled in a Spex mixer EXAMPLES 9 at a 5 percent solids concentration in tetrahydrofuran Milled Diane Blue pigment, at a concentration of (TI-IF) and then coated at 1 mil wet gap on rough stock percent by weight, was dispersed in a wide variety of aluminum. They were then overcoated with a 1:1 by polymersensitizer combinations, and the .resulting mix- -weight mixture of trinitrofluorenone and Mylar adhetures coated on a conductive substrate at thicknesses sive 49,000 dissolved in THF, at a thickness of about ranging from 12 to microns. The plates were oven- 10 microns. The pigment structures are as lettered 3 cured at 55 percent C for 2 hours, and the electrometabove in Examples 6-28. The electrometric data are ric data shown in Table V were obtained. In all cases,

shown in Table IV. full tungsten light was employed.

TABLE V EX. SENSITIZER 3 POLYMER C.A. T k NO.

1,8-eihydroxy- 25 polyvinyl- 75 410 480 0.95 1.0

anthraquinone carbazole 36 ditto 50 poly-4-vinyl- 50 370 410 2.0 2.7

dibenzofuran 37 ditto 5O polyketone 50 350 410 0.6 0.9

1 (PK 252) 38 ditto 50 poly-(p- 50 220 220 1.2 1.2

phenoxyphenyl) sulfide 39 ditto 50 poly-Z-vinyl 50 450 5 10 2. 1 -2. 1

- fluorene v 40 1,4-naphtha- 50 pol vinyl- 50 380 350 4.5 2.2

quinone car azole 41 ditto 50 po1y-4-vinyl- 50 420 350 10.1 10.0

benzofuran 42 ditto 50 polyketone 50 250 240 1.9 1.5

(PK 252) 43 ditto 5O poly-(p- 50 380 380 2.0 2.0

phenoxy-phenyl sulfide 44 ditto 50 poly-2-vinyl 50 380 350 1.1 1.2

fluorene 45 ditto po1y-2-vinyl 50 410 500 3.0 2.5

naphthalene 46 Benzlalanthra- 50 polyvinyl- 50 370 300 0.9 1.2

cane-7. l 2-dione carbazole 47 ditto 50 po1y-4-vinyl- 50 340 350 9.0 9.0

dibenzofuran 48 ditto 50 polyketone 50 380 320 5.0 5.0

(PK 252) 49 ditto 50 po1y(p-phenoxy 50 350 290 4.0 4.0

, -pheny1 )sulfide 50 ditto 50 2-viny1- 50 410 330 8.0 10.0

naphthalene 51 9-dicyanomethypolyvinyl- 25 630 720 1.2 1.1

lene-2,4,7- carbazole trinitrofluorene TABLE V Continued EX. SENSlTIZER POLYMER C.A. T A

NO. 7r 7:

52 9-dicyunomethyl- 75 polyvinyl- 25 340 280 l .6 1.7

ene-2,4.7- carbazole trinitrofluorene 53 ditto 75 polyketone 25 370 450 2.5 2.5

(PK 252) 54 3,5-dinitrobenpolyvinyl- 95 165 280 0.8 0.45

zoic acid carbazole 55 ditto 5 poly-4-vinyl- 95 520 580 10.0 10.0

dibenzofuran 56 ditto 5 polyketone 95 620 650 2.4 l .9

(PK 252) 57 ditto 5 poly (p-phen- 95 410 540 3.0 3.0

oxy-phenyl) sulfide 58 ditto 5 2-vinyl- 95 420 400 2.0 2.0

naphthalene 59 tetrachloro poly-4-vinyl- 90 980 680 10.0 10.0

phthalic bibenzofuran anhydride 60 ditto l0 polyketone 90 410 3 80 2.0 2.0

(PK 252) 6| ditto l0 poly-2-vin yl 90 840 930 2.5 l .8

naphthalene 62 tetranitrol0 poly-4-vinyl 90 390 480 l .4 2.0

naphthalene dibenzofuran 63 ditto l0 polyketone 90 440 570 l l 0.9

(PK 252) 64 ditto l0 poly-2-vinyl 90 280 3 l 0 2.0 l .2

naphthalene 65 tetracyanoethy- 2 polyvinyl- 98 120 120 l .2 0.8

lene carbazole 66 ditto 2 polyketone 98 370 280 5.0 5.0

(PK 252) 67 trinitro-phenpolyvinyl- 75 170 200 2.6 2.5

anthraquinone carbazole 68 trinitro-phen- 25 poly-4-vinyl 75 170 200 2.6 2.5

anthraquinone dibenzofuran 69 ditto 25 polyketone 75 450 600 2.0 2.5

EXAMPLES 70-98 Pigment M Additional experiments were run using pigments with the structures shown below:

Pigment J NH Pigment N Pigment K O H OH c1 Pigment L Pigment O o 0 H OH Cl OH Br Q o N N== N c1 Pigments .1 through Q inclusive were measured in four different types of plates, numbered Plates -8 inclusive. In each case the milled pigment was coated on a conductive substrate. In Plate 5, the pigment with no binder and no overcoat was used. (Measurements in this system were with full tungsten light. In all other systems, measurements were with 1.16 NDS and 0.6.) In Plate 6, 5 percent by weight of the milled pigment was mixed with a 1:1 molar mixture of TNF and polyvinyl carbazole. In Plate 7, 10 percent by weight of the pig ment was mixed with a mixture of TNF (20 percent) and polyvinyl carbazole. In Plate 8, 10 percent of the pigment by weight was mixed with a 1:1 by weight mixture of TNF and Mylar adhesive-49,000.

Pigment .1

Example No. Plate T V2 C.A.

Pigment K Example No. Plate T V2 C.A.

74 5 Not available 75 6 3.3 0.75 220 300 76 7 5.4 7.0 550 560 77 8 5.4 3.0 600 700 Pigment L Example No. Plate T V2 CA.

Pigment M Example N0. Plate T /2 CA.

Continued Pigment N Example No. Plate T A. CA.

Pigment 0 Example No. Plate TVz CA.

Pigment P Example No. Plate T /2 CA.

Pigment Q Example No. Plate T CA.

wherein A is selected from the group consisting of:

H lil (6 OH (a) l?-? and (b) NC v I R wherein R is selected from the group consisting of lower alkyl and lower alkyl, and X and Y each selected from the group consisting of:

13 H, CH OCH OC H OH, Cl and Br, with the pigment particles being present in an amount of from 5 percent to percent by weight of the total weight of the pigment particles plus the binder material.

2. A process as claimed in claim 1 wherein the particle size of the pigment is less than about 1 micron.

3. A process as claimed in claim 1 wherein the pigment is present as a layer overcoated with a binder layer capable of transporting the charge.

4. A process as claimed in claim 1 wherein the pigment is dispersed in a binder which is a charge transport material.

5. A process as claimed in claim 4 wherein the binder is photoconductive per se.

6. A process as claimed in claim 4 wherein trinitrofluorenone has been added to the binder.

7. A process as claimed in claim 1 wherein the pigment is 3,3 dichlor0-4,4' diphenyl bis-( 1 -azo- 

1. IN AN ELECTROPOTOGRAPHIC REPRODUCTION PROCESS WHICH COMPRISES THE STEPS OF UNIFORMLY CORONA CHARGING A PHOTOCONDUCTOR ON A CONDUCTIVE SUBSTRATE AND IMAGEWISE EXPOSING THE PHOTOCONDUCTOR TO LIGHT, THE IMPROVEMENT ACCORDING TO WHICH THE PHOTOCONDUCTOR COMPRISES PIGMENT PARTICLES AND BINDER MATERIAL, WITH THE PIGMENT PARTICLES BEING PRESENT AS POLYMOLECULAR AGGREGATES LESS THAN FIVE MICRONS IN SIZE AND HAVING A FORMULA
 2. A process as claimed in claim 1 wherein the particle size of the pigment is less than about 1 micron.
 3. A process as claimed in claim 1 wherein the pigment is present as a layer overcoated with a binder layer capable of transporting the charge.
 4. A process as claimed in claim 1 wherein the pigment is dispersed in a binder which is a charge transport material.
 5. A process as claimed in claim 4 wherein the binder is photoconductive per se.
 6. A process as claimed in claim 4 wherein trinitrofluorenone has been added to the binder.
 7. A process as claimed in claim 1 wherein the pigment is 3,3'' dichloro-4,4'' diphenyl bis-(1''''-azo-2''''hydroxy-3''''-naphthanilide).
 8. A process as claimed in claim 1 wherein the pigment is 3, 3''dimethoxy-4,4''diphenyl bis-(1''''azo-2''''hydroxy-3''''-naphthanilide).
 9. A process as claimed in claim 1 wherein the pigment is 3, 3''dimethyl-4,4''diphenyl bis-(1''''azo-2''''hydroxy-3''''-naphthanilide).
 10. A process as claimed in claim 1 wherein the pigment is 3, 3''dibromo-4,4''diphenyl-bis-(1''''azo-2''''hydroxy-3''''-naphthanilide).
 11. A process as claimed in claim 1 wherein the pigment is 4,4'' diphenyl-bis-(1''''-azo-2''''hydroxy-3''''-naphthanilide). 